LONDON (AP) - The U.K. tightened up rules Saturday on mask-wearing and on testing of international arrivals after finding two cases of the new potentially more contagious omicron variant of the coronavirus as governments around the world sought to shore up their defenses.Amid fears that the recently identified new variant has the potential to be more resistant to the protection offered by vaccines, there are growing concerns that the pandemic and associated lockdown restrictions will persist for far longer than hoped.Prime Minister Boris Johnson said it was necessary to take "targeted and precautionary measures" after two people tested positive for the new variant in England, and that these will be reviewed in three weeks when scientists.